The present invention relates to the continuous casting of molten steel transferred to a tundish of a continuous caster by a succession of ladles where molten steel flows from a ladle into the tundish and then into one or more continuous casting molds. Maintaining a steady flow of molten steel into the one or more continuous casting molds is essential, so as not to disturb a delicate balance of sufficient cooling for the necessary containment of a liquid steel core in the newly formed solid shell, and casting speed required for proper metal solidification. The temperature of the molten steel is critical to the casting process, and so it is imperative that a ladle is tapped for the casting process according to a schedule established to prevent the cooling of the molten steel below a desired casting temperature and to avoid the need to return the molten steel to the steel making furnace for reprocessing and the consequential stoppage of the casting process. The volume of molten steel in the tundish is selected to always maintain an operating level even when floating out of slag impurities and during an interruption to the flow of molten steel from one ladle during sequencing of ladles to the caster to reestablish the flow of molten steel by a second ladle.
A typical sequencing of ladles is started by first increasing the flow of molten steel from a first ladle before the ladle is empty to raise the liquid steel level in the tundish above an operating level. When the flow from the ladle changes from molten steel to slag, the slidegate is closed to stop the flow of slag. A pouring shroud is disconnected from the ladle slidegate and the ladle is moved away from the casting position. At the same time a second ladle is brought into the casting position and a pouring shroud is connected to the slidegate of the second ladle whereupon opening of the slidegate initiates the flow of molten steel into the tundish. The entire sequence, from the stoppage of the flow of molten steel in one ladle to the establishment of a flow of molten steel in a replacement ladle, must be completed before the liquid level in the tundish has been depleted to a certain critical level, below which the quality of the cast steel strand is adversely affected. The sequence of changing the supply of molten steel from one ladle to another is normally accomplished within a very safe time margin. Two typical devices employed in the efficient exchange of ladles are ladle cars and a ladle turret.
The present invention is addressed to the management of a ceramic pouring shroud having the general form of a tube arranged to isolate the stream of molten steel from contamination, for example, with oxygen and nitrogen in the atmosphere while passing from the ladle to the tundish. Such a ceramic pouring shroud is supported and moved by operation of a manipulator that includes synchronous movement of the ladle and ceramic pouring shroud after pressing the upper end of the ceramic pouring shroud into sealing contact the with the slide gate of the ladle. The sealing contact is maintained while the ladle is moved with into the casting position wherein the lower end of the ceramic pouring shroud is partly submerged in the molten steel in the tundish. The environment and conditions wherein these operations by the manipulator are carried out are very adverse because of the extreme temperature and the very limited amount of time available to establish and maintain the essential gaseous sealed relation between the ladle and the tundish. A need therefore exists for verifying the sufficiency of the gaseous tight seal between the ceramic pouring shroud and the ladle to prevent the ingress of atmospheric gaseous while molten steel is flowing in the shroud from the ladle to the tundish. A need also exists to establish and maintain an inert atmosphere in the cavity of the ceramic pouring shroud at least until the flow of molten steel commences in the ceramic pouring shroud but preferable continuously while molten steel flows from the ladle to the tundish.
Accordingly, it is an object of the present invention to provide a method and apparatus for verifying the sufficiency of the gaseous tight seal between the ceramic pouring shroud and a ladle for molten steel incident to the operations of a manipulator employed to hold the ceramic pouring shroud against a ladle containing molten steel.
It is a further object of the present invention to provide a method and apparatus to supply establish and maintain an inert atmosphere in the cavity of the ceramic pouring shroud at least until the flow of molten steel commences in the ceramic pouring shroud from a ladle to a tundish.